Comparison of serum-free thyroxine concentrations determined by standard equilibrium dialysis, modified equilibrium dialysis, and 5 radioimmunoassays in dogs

Sara Schachter, Richard W Nelson, Catherine Scott-Moncrieff, Duncan C. Ferguson, Tracey Montgomery, Edward C Feldman, Larry Neal, Philip H Kass

Research output: Contribution to journalArticle

23 Scopus citations

Abstract

Measurement of serum-free thyroxine (fT4) concentration provides a more accurate assessment of thyroid gland function than serum thyroxine (T4) or 3,5,3′-triiodothyronine (T3). Techniques for measuring serum fT4 concentration include standard equilibrium dialysis (SED), radioimmunoassay (RIA), and a combination of both (modified equilibrium dialysis [MED]). This study compared results of serum fT4 measurements by means of SED, MED, and 5 RIAs in 30 healthy dogs, 10 dogs with hypothyroidism, and 31 euthyroid dogs with concurrent illness for which hypothyroidism was a diagnostic consideration. Serum fT4 concentrations were comparable when determined by the SED and MED techniques, and mean serum fT4 concentrations were significantly (P < .01) lower in dogs with hypothyroidism than in healthy dogs and euthyroid dogs with concurrent illness. Significant (P < .05) differences in fT4 concentrations were identified among the 5 RIAs and among the RIAs and MED and SED. Serum fT4 concentrations were consistently lower when fT 4 was determined by the RIAs, compared with either equilibrium dialysis technique. Serum fT4 concentrations were significantly lower (P < .01) in dogs with hypothyroidism than in healthy dogs for all RIAs; were significantly lower (P < .05) in dogs with hypothyroidism than in euthyroid dogs with concurrent illness for 4 RIAs; and were significantly lower (P < .01) in euthyroid dogs with concurrent illness than in healthy dogs for 4 RIAs. RIAs had the highest number of low serum fT4 concentrations in euthyroid dogs with concurrent illness. This study documented differences in test results among fT4 assays, emphasizing the importance of maintaining consistency in the assay used to measure serum fT4 concentrations in the clinical or research setting.

Original languageEnglish (US)
Pages (from-to)259-264
Number of pages6
JournalJournal of Veterinary Internal Medicine
Volume18
Issue number3
DOIs
StatePublished - May 2004

Keywords

  • Free thyroxine
  • Hypothyroid
  • Sick euthyroid

ASJC Scopus subject areas

  • veterinary(all)

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